In recent years, media used for optically recording information have been proposed and developed that include an optical disk, an optical card, and an optical tape. Particular attention has been given to an optical disk as a medium that allows large-capacity and high-density recording and reproduction of information.
Among the forms of rewritable optical disks is a phase change optical disk. A recording film used in the phase change optical disk is brought into either an amorphous state or a crystalline state depending on conditions of heating and cooling by a laser beam. There is reversibility between the amorphous state and the crystalline state. The recording film varies in optical constants (refractive index and extinction coefficient) depending on whether the recording film is in the amorphous state or the crystalline state. In the phase change optical disk, these two states are formed selectively on the recording film according to an information signal. As a result of this, optical variations (variations in transmittance or reflectance) are caused and used to perform recording and reproduction of the information signal.
In order to obtain the above two states, an information signal is recorded by the following method. A laser beam (power level Pp) focused by an optical head is irradiated onto a recording film of an optical disk in a pulse-like state (referred to as a recording pulse). A temperature increased beyond the melting point causes the recording film to melt. The melted portion is cooled rapidly as the laser beam passes therethrough and turned into a recording mark (referred to also as a mark) in an amorphous state. The power level Pp is referred to as peak power. On the other hand, when a laser beam (power level Pb, Pb<Pp) is focused to be irradiated onto the recording film, which has such an intensity as to increase the temperature of the recording film to a temperature higher than the crystallization temperature but lower than the melting point, a beam-irradiated part of the recording film is brought into a crystalline state. The power level Pb is referred to as bias power. The peak power and the bias power are referred to as recording power, collectively.
In the foregoing manner, a recording pattern of the recording mark of an amorphous region that corresponds to a recording data signal and a mark non-forming part of a crystalline region (referred to as a space) is formed on a track of the optical disk. By the use of differences in optical characteristics between the crystalline region and the amorphous region, the information signal can be reproduced.
Recently, the mark edge recording (referred to also as the PWM recording) method has been in wider use than before in place of the mark position recording (referred to also as the PPM recording) method. The mark position recording allows only a position of a recording mark itself to have information; while the mark edge recording allows both front and back ends of a recording mark edge to have information, thereby being advantageous in improving recording linear density.
Particularly, in the mark edge recording method, recording is performed in such a manner that a recording pulse generated in recording a long mark is resolved into a plurality of recording pulse trains (referred to as a multiple pulse), and that a first pulse (referred to as a front-end pulse) is made wider than an intermediate pulse and a last pulse (referred to as a back-end pulse). The recording is thus performed with the following in mind. In recording a back part of a mark, a recording film is fed with less heat than that in the case of recording a front part of the mark in consideration of the influence of excess heat transmitted from the front part of the mark. Accordingly, distortion in the shape of the recording mark is reduced, whereby the mark is recorded with increased accuracy.
In the meantime, in view of an optical disk being a replaceable recording medium, a device for recording and reproducing optical disks is required to allow stable recording and reproduction with respect to a plurality of optical disks different from one another. However, even optical disks manufactured under the same conditions may vary from one another in the recording power that is optimum for recording and reproduction due to variations in thermal characteristics attributable to variations caused during manufacturing and changes over time. Further, laser beam power to reach a recording film of an optical disk may vary due to staining on the surface of a substrate of the optical disk and a decrease in transmission efficiency of an optical system and variations in an operating condition of a recording and reproducing device.
Furthermore, in the mark edge recording method, variations in thermal characteristics of an optical disk have an influence on a forming condition of a recording mark itself and the degree of thermal interference among recording marks. That is, even recording marks formed as a result of recording in the same recording pulse waveform vary in shape from one disk to another. Thus, a recording mark edge may shift from an ideal position to cause degradation of a reproduced signal depending on a disk that is used.
Therefore, it is requested to allow a recording mark to be recorded in ideal edge positions irrespective of which disk is used by optimally correcting recording power, a front-end pulse edge position, and a back-end pulse edge position with respect to each disk.
An example of a method for accurately recording and reproducing an information signal by correcting optimum power level of a laser beam, a front-end pulse edge position, and a back-end pulse edge position as described above has been disclosed in JP 2679596 B. In the example, combinations of a length of a recording mark (referred to as a self mark length) and lengths of spaces preceding and following the recording mark (referred to as a preceding space length and a following space length, respectively) are organized into combination tables, and with respect to each element in the combination tables, a front-end pulse edge position or a back-end pulse edge position is corrected.
Furthermore, a method for determining optimum recording power from power dependence of a bit error rate has been disclosed in JP 9(1997)-63056 A. Further, the following method has been disclosed in JP 6(1994)-195713 A. Prior to recording of an information signal that is performed in starting up a recording and reproducing device and in introducing an optical disk, a test recording using a data pattern having a certain period of time (referred to as a test pattern) is performed. Then, a test signal as a result of the recording is reproduced, and a resultant reproduction signal is measured to determine a shift amount of a recording mark edge. A front-end pulse edge position and a back-end pulse edge position are corrected accordingly.
However, in the conventional methods described above, in introducing an optical disk, for example, a test recording always results in following the same sequence of steps irrespective of the type of optical disk that is used. Accordingly, when the recording power, the front-end pulse edge position, and the back-end pulse edge position retained as initial values in a recording and reproducing device are optimum with respect to an introduced optical disk, a test recording results in having substantially redundant steps. As a result, it takes much time for the recording and reproducing device to be brought into a state where an information signal actually can be recorded, which has been disadvantageous. Particularly, determining a front-end pulse edge position and a back-end pulse edge position requires many steps of test recording, and thus the time taken to obtain a state where an information signal can be recorded is considerable.
Furthermore, in some cases, even when a front-end pulse edge position and a back-end pulse edge position are corrected during steps of a test recording using a test pattern, the corrected edge positions may not be sufficiently optimum in actual recording of an information signal. As a result, the test recording using a test pattern alone does not allow recording of an actual information signal to be performed with sufficient accuracy, which has been disadvantageous.
Furthermore, in the conventional methods, when recording pulse trains that depend on a mark of an information signal are generated to record information, in some cases, a front part and a back part of a recording mark may be distorted asymmetrically with each other due to variations in thermal characteristics of an optical disk. As a result, a reproduction signal is distorted, so that even when a front-end pulse edge position and a back-end pulse edge position are optimized by a test recording, an information signal can not be recorded with sufficient accuracy, which has been disadvantageous.